Hydraulic system



March 25, 1958 R. H. GOVAN ET AL 2,827,763

HYDRAULIC SYSTEM Filed May 20. 1955 3 Sheets-Sheet 1 INVENTORS 7? 96am;Jm% JM BY A1 ATT RNEY March 1958 R. H. GOVAN ET AL 2,827,763

HYDRAULIC SYSTEM Filed May 20, 1955 '5 Sheets-Sheet 3 FIG. 4

g Q INVENTORS j/raldJfieck BY A RNEY United States Patentuse HYDRAULICSYSTEM Roy H. Govan, Hoboken, N. 1., and Harold J Meek, Staten Island,N. Y., assignors to Jaroco Engineering (10., Hohoken, N. 3., acorporation of New Jersey Application May 20, 1955, Serial No. 509,724

Claims. (Cl. 60-51) The present invention relates to a hydraulic system.More particularly, the present invention relates to a selfcontainedhydraulic system which includes a hydraulic fluid accumulator thatcommunicates with a motor-pump unit, the motor pump unit beingresponsive to various conditions of load and to fluid under pressure inthe accumulator, thereby being alternately operated as a motor and as apump for effecting the rotation of the shaft of the unit.

It is the general practice in power operated devices that utilizehydraulic fluid as a motive fluid to direct the motive fluid underpressure to a motor or the like to thereby perform a particularoperation such as, for example, lifting a load. It is desirable in suchsystems to employ a self-contained hydraulic device wherein a hydraulicmotive fluid may be maintained under pressure and distributedperiodically to aid in accelerating a vehicle shaft or for controllingthe rotation of a shaft subjected to loads. Prior to the instantinvention, the heretofore i nown hydraulic systems did not provide forthe accumuation of hydraulic fluid under pressure wherein the fluidunder pressure could be effectively controlled when the system wassubjected to a variety of conditions.

It is therefore an object of the present invention to provide ahydraulic system wherein hydraulic motive fluid contained therein iseflectively controlled during all conditions of operation of the system.

Another object of the present invention is to provide a hydraulic systemfor effecting the operation of a motor-pump unit, motive fluid containedin the system being controllably directed to said motor-pump unit forcontrolling the operation thereof.

Still another object of the present invention is to provide a hydraulicsystem which includes an accumulator for receiving motive fluid therein,the motive fluid being controlled for effectively operating a motor-pumpunit.

Still another object of the present invention is to provide anaccumulator for a hydraulic system which is adapted to maintain a motivefluid therein at a predetermined pressure, the motive fluid underpressure being utilized to operate a motor-pump unit.

Still another object of the present invention is to provide a hydraulicsystem wherein a variable displacement pump is employed for directing amotive fluid to a hydraulic fluid accumulator, the motive fluid beingmaintained in the accumulator at a predetermined pressure during variousoperating conditions of the hydraulic system.

Still another object of the present invention is to provide a hydraulicsystem wherein a motive fluid maintained in a hydraulic fluidaccumulator under pressure is adapted to be directed to a motor-pumpunit operatively connected to a vehicle engine shaft, therebyaccelerating the engine shaft.

Still another object of the present invention is to provide a hydraulicsystem wherein a motor-pump unit is responsive to the load on the shaftthereof to automatically control the supply of a motive fluid underpressure to said unit for operating the unit as a pump or motor.

Still another object of the present invention is to provide a hydraulicsystem wherein a motor-pump unit is manually controlled for reversingthe rotation thereof, thereby controlling the operation of the shaft ofthe unit under various conditions of load.

Other objects and the nature and advantages of the instant inventionwill be apparent from the following description taken in conjunctionwith the accompanying drawings, wherein:

Fig. 1 is a diagrammatic illustration of one form of the hydraulicsystem embodied in the present invention;

Fig. 2 is a diagrammatic illustration of a modified form of thehydraulic system illustrated in Fig. 1;

Fig. 3 is a sectional view of the control device for controlling theoperation of the variable displacement pump illustrated in Fig. 2; and

Fig. 4 is a diagrammatic illustration of a further modified form of thehydraulic system embodied herein.

Referring now to the drawings, and particularly Fig. 1, one form of theinvention is illustrated diagrammatically therein. The hydraulic systemillustrated in Fig. 1 is intended for use as a power and braking deviceand it is intended to be employed particularly in connection withlifting appaartus such as, for example, deck winches associated with acargo vessel. It is understood, however, that the hydraulic systemdisclosed in Fig. 1 may be utilized in connection with other apparatuswhenever power and braking needs are required. The hydraulic systemillustrated in Fig. 1 includes a plurality of motor-pump units fill, 12and 14 which are shown operatively connected in parallel relation.Although only three of the motor-pump units are shown in the drawings,it is contemplated to utilize as many of the units as practicably neededin connection with the load requirements of the system. The motor-pumpunits 10, 12 and 14 are of the variable displacement type which includesa rotor provided with variable stroke pistons. The specific constructionof the units is illustrated on page 6 of Air and Oil HydraulicComponents, Condensed Catalog 1101, published by the Hydraulic PressManufacturing Co.

It is believed suflicient for the underestanding of the operation of thepresent invention, that only the general description of these units beset forth herein. It is understood that in order to effect the rotationof a variable displacement pump the stroke of the pistons associatedtherewith must be altered. When altering the stroke of the pistons, apiston carrier ring is moved in eccentric relation with respect to themotor-pump unit rotor and the piston stroke and rotation of the unit isaccordingly changed. The unit may be completely reversed in rotation bychanging the stroke of the pistons so that the discharge port of theunit is caused to operate as the suction or inlet side. As shown in Fig.1, in order to vary the stroke of the pistons associated with each ofthe motor-pump units, a manually operated lever 16 is provided and isoperatively secured to a shaft 18 which is operatively connected to thedisplaceable pistons for effecting the stroke varying operation. Byvarying the stroke of the pistons in each unit, the rotation of therotor associated therewith is effected.

Communicating with the discharge or the suction port (depending on thedirection of rotation) of the motorpump units it 12, 14, through fluidconduits 20, 21, 22, respectively, and fluid conduits 23 and 24 is areservoir 25 that is adapted to contain hydraulic fluid therein. Any

one of the units 19, 12 and 14, which communicate with the fluid conduit24. through the common fluid conduit 23, may be shut off fromcommunication therewith as desired by block valves 26, 27 and 28,respectively. The

opposite or suction side, or alternatively, the. discharge side, of theunits 10, 12" and 14 communicates with a hydraulic accumulator 30through fluid conduits 31, 32 and 33, respectively, and fluid conduits34 and 35. As shown, block valves 36, 37 and 38 are located in theconduits 31, '32 and 33 and are provided for shutting off units 10, 12and "1 4 from communication with the conduit 34, as

' desired. 7

1 The hydraulic accumulator 30 is provided with a pis ton 40- that; ineffect, floats therein and divides the accumulator into an upper and alower chamber '42 and 44. Agas under pressure is; introduced into thespace or chamber 42 and is adapted to subject the piston 40 toapredeterminedpressure. It is understood that the gas located in thespace 42 may be retained at any desired pressure dependent upon therequirements of the system. It is seen that the bottom space orchamber'44 of the accumulator below the piston 40 may be filled with ahydraulic-"fluid until the pressure, in the space 44; is equal to thepredetermined pressure of the gas in the space 42. In thiscondition,-the pressures on the piston 40 are, equalized and the pistonwill float midway in the accumulator 30. In order to. introducehydraulic fluid into the space 44 of the accumulator 30, a variabledisplacement pump 46is provided. The pump 46 maybe driven by anysuitable prime mover coupled thereto; an electric motor 48 beingprovided in the present instance. The variable displacement pump 46 isequipped with a pressure holding control that:automatically reduces pumpdelivery to zero when a predetermined pressure has been reached in theline communicating therewith. The desired pressure is obtained byregulating a hand wheel 50 that controls the setting of a piston-typerotor. As shown, the variable displacement pump 46 communicates with thehydraulic accumulator 30 through a fluid conduit 54 and the coni duit35' joined to the conduit 54, and is adapted to receive hydraulic fluidfrom the reservoir 25 which communicates. therewith through the fluidconduit 24 and a conduit52'; Itis seen that hydraulic fluid maybe'supplied to the space 44 in the accumulator 30 by the variabledisplacement pump 46 by way of fluid conduits 54 and 35 until theypressure of the hydraulic fluid is equal to the p essnreof the gas inspace 42. 'At this point, the variable displacement pump 46 floats onthe line, that is, does not deliver fluid, since pump delivery has beenreduced to zero. Itis'seenthat the variable displacement pump 46 isalways ready to supply or make up the hydraulic fluid in the accumulator30 whenever the pressure in the space 44td'rops. below the predeterminedamount;

In the operation. of the hydraulic system shownin Fig. 1, anyone of themotor-pump units 10, 12 or 14 may be operated independently, or all ofthe units may be operated simultaneously,if so desired. For purposes ofillustrating the invention, only the unit will be included in thedescription of the operation. It is assumed that the variabledisplacement pump 46 has supplied the accumulator 30 with the amount ofmotive fluid necessary to reachthe predetermined pressure in theaccumulator andthat the pump 46' is floating on the line If themotor-pump unit 10 is then required to lift aload such as, for-example,when a cargo is to be lifted from a dock into'theihold of a ship, themanually operated lever 16 is moved to control the variable displacementmotorpump unit 10 such that motive fluid from the hydraulic accumulator30' is introduced thereto by way of the fluid conduits'35j34 and 3 1.The unit 10 is then operated as a motor and the shaft thereof is causedto rotate for operating a winch or the like. operatively connectedthereto for lifting the load. As the shaft of the unit 10 rotates,energy is accumulated in the lifted load and the motive fluid isdirected to the reservoir by way of the fluid conduit 24. Since thepressure of the motive fluid 1n the accumulator will be reduced belowthe pre set amount during the lifting operation thevariablecapacity pump46 will then respond to the decreased pres- '4. sure in the line to.supply the. required amount of motive fluid to the accumulator 30 untilthe pro-set pressure is again reached, When the winch connected to theshaft of the motor-pump unit has lifted the load to the desired level,it is then required to lower the load and a braking operation isnecessary. By controlling the manual control lever 16 and varying thestroke of the pistons in the motor-pump unit 10, the energy accumulatedin the load lifted by the unit 10 will cause the rotor thereof to rotatein a reverse direction, thereby operating the unit as a pump, The loadis then lowered with a braking action and, in addition, the unitoperates as a pump to pump fluid from the reservoir 25 through conduits24 and i 20 and then through conduits 31, 34 and to return the motivefluid to the accumulator 39. It will be seen that this will increase thequantity and pressure of motive fluid in accumulator 30 'to a pointconsiderably above the pre-set amount. Consequently, the variablecapacity pump 46 will be held inactive until the motive fluid, thusaccumulated is utilized in a subsequent lifting operation. Thus, all ofthe energy in the form of the'hydraulic fluid under pressure is returnedto the hydraulic accumulator 30 with the exception of that lost due tomechanical and fluid friction. Since the motive fluid in space 44 of theaccumulator 30 is not fully returned by the unit 10 because of theaforesaid losses, the variable capacity pump 46 will then respond to theresultant decreased pressure in the line to supply the required amountof motive fluid to the accumulator 36 until the predetermined pressureis again reached. The accumulator is then fully charged and the fluidcontained therein under pressure may again be directed to the motor-pumpunit 10 by controlling.

the manually operated lever 16 for effecting a power operation. In orderto provide for means for returning fluid to the reservoir 25, in theevent that the motorpumpunits 10, 12 and 14, during a braking operation,over-supply the accumulator 30, the reservoir 25 is connected to arelief valve 56 through a fluid conduit 58, the relief valve 56communicating with the fluid conduit 34 which, in turn, communicateswith the accumulator 30, through conduit 35. It is seen that any one ofthe units 10, 12, 14 may be operated independently of the other or theunit 19 may be operated in parallel and simultaneously with both oreither of the units l2 and 14. "It is also seen that the manuallyoperated lever 16 may be controlled by electric, pneumatic or hydraulicservo systems positioned at a remote point. single operator may beemployed to control a plurality of winches for loading a ship or thelike.

Referring now to Fig. 2, a modified form of the system shown in Fig. lis illustrated and is adapted to be used particularly in connection withtow lines associated with tugs. In a towing operation, the tow line iswound on a winch and is connected to the load or ship being towed and isnormally subjected to a varying tension. On occasion, due to thevariations in load during the towing operation, the line will bepayed-out or payed-in, depending upon the particular conditions involvedwhich vary the tension in the line. in order to automatically compensatefor the paying-out and paying-in, by varying the tension in the towline, the system illustrated in Fig. 2 is provided. As. shown, amotor-pump unit 60 is provided and is operatively coupled to a variabledisplacement pump 62 through a shaft 64. The pump 62 is of that typedescribed above in connection with Fig. l and is adapted toautomatically maintain a variable compensating pressure in anaccumulator described below. Rotation of the shaft 64 is adapted toautomatically control the. variable displacement pump 62, and this feature will be described in detail hereinafter. The motorpump unit 60communicates with a reservoir 66 through a fluid conduit 68 and furthercommunicates with the variable displacement pump 62 through .a fluidconduit 70. The variable'displacement pump 62 communicates with ahydraulic accumulator 72"through fluid conduits Thus, a V

'74 and 76, the accumulator being of that types described above inconnection with Fig. 1. The hydraulic accumulator 72 also communicateswith the motor-pump unit 60 through fluid conduits 76, 78 and 80 and arelief valve 82 is provided communicating with the fluid conduit 78through a fluid conduit 84. The relief valve communicates with thereservoir 66 through a fluid conduit 86 and is adapted to return fluidto the reservoir in the event a predetermined unsafe pressure in theaccumulator 72 is about to be reached. A load in the form of a winch 88is coupled to the motor-pump unit 66 through a shaft 90 and isresponsive to the rotation of the motorpump unit 6:? to pay-in andpay-out a tow line 92 associated therewith.

In operation, the variable displacement pump, which is driven by anelectric motor 94, coupled directly thereto, is operated to directmotive fluid to the accumulator 72 until a predetermined pressure isreached therein. it is arbitrarily assumed that the load on the line 92is 8,000 pounds at normal operating conditions, that is, the tension inthe line 92 under the specific load condition is 8,000 pounds. Assumingnow that the tow line 92 begins to pay-out, due to an externalcondition, the tension in the line 92 is thereby varied and themotorpump unit 69, which is operatively connected to the winch $8, isrotated in a direction to pump motive fiui from the reservoir 66 to theaccumulator 72 by way of fluid conduits 8d, 78 and 76, thereby buildingup the pressure in the accumulator 72. At this stage, the variabledisplacmeent pump 62 is running idle on the line since the pressure inthe accumulator is above the preset pressure setting therein. As themotor-pump unit 60 is rotated in a direction to pump motive fluid fromthe reservoir 66 to the accumulator 72, the pressure setting on thevariable capacity pump. 62 is changed, this being accomplished by therotation of the shaft 64.

Referring now to Fig. 3, a detail of the pressure setting device for thevariable displacement pump 62 is shown and includes a hand-operatedwheel 95 that has a shaft portion 96 formed integral therewith which isexternally threaded at 97, the shaft portion 96 being received by thehousing of the pump 62 and terminating in a flange 98. The hand wheel 95is also internally threaded and is adapted to threadably receive foraxial movement therein a shaft 99. The shaft 99 slidably engages acoupling 100 (Fig. 2) that is secured to the shaft 64, the shaft 99being capable of longitudinal movement within the coupling 10%, thepurpose of which will be described below. Although the coupling 16% isshown directly connecting shaft 64 to shaft 99, it is understood that aconventional clutch may be provided in place of the coupling which wouldallow for unimpeded operation of the tow line 92 when the towingconnection is being established initially.

Engaging the flange 93 of the shaft portion 96 is a spring 191 thatabuts against a piston 102 that is adapted to control the pressuresetting of the pump 62. Engaging the lower end of the shaft 99 andpositioned within the spring 181 is a smaller spring 163 that also abutsagainst the piston 102 for controlling the pressure setting of the pump62. It is seen that the manual control or wheei 95' may be rotated toset the pressure setting on the pump 62 to that the pump supplies fluidto the accumulator until the pro-set pressure is reached. This pressuresetting is varied upon rotation of the shaft 64, which rotates the shaft99. Rotation of the shaft 99 within the stationary shaft portion 96causes the shaft 99 to translate longitudinally, this longitudinalmovement of the shaft 99 being taken up within the coupling 1%. Thelongitudinal movement of the shaft 99 thereby actuates the piston 162which changes the pressure setting on the pump 62, thereby compensatingfor various loads on the motor-pump unit 69. By controlling the pressuresetting of the pump 62, the pressure of the fluid directed to theaccumulator 72 and communicating with the pump 62 will accordingly bevaried. Thus, when the line 92 is payed-out to operate the motor-pumpunit 60 as a pump, the shaft 64 will be rotated to increase the pressuresetting on the pump 62. It is seen that at this stage the pump 62 willnot operate until the pressure determined by the new setting is reachedsince the accumulator pressure is greater than the new setting of thepump 62. It is seen that as the motor-pump unit 60 pumps the fluid intothe accumulator, the pressure setting in the pump 62 will becorrespondingly increased. If the load on the tow line 92 is changed tocause the load to decrease below a normal amount or below 8,000 pounds,the motor-pump unit 60 will then operate as a motor, causing motivefluid in the accumulator 72 to be discharged through fluid conduits 76,78 and 80 and thereby causing the winch 88 to Wind in the cable tomaintain the normal tension on the line. The motive fluid is returned inthis operation to the reservoir 66. As the tow line 92 pays-in and themotor-pump unit 60 is thereby rotated by the motive fluid from theaccumulator 72, the shaft 64 is rotated to decrease the pressure settingon the pump 62. As the tow line 92 continues to pay-in, the setting onthe pump 62 will be normally above the predetermined pressure in theaccumulator 72 since the winch 88, due to frictional and hydrauliclosses, has not payed-in the line 92 that amount which it payed-out.However, since the fluid in the accumulator 72 has caused operation ofthe motorpump unit 60 to reduce the pressure in the accumulator 72 thatamount necessary to maintain an 8,000-pound pull on the line 92, thepump 62 will then function to augment the accumulator 72 to produce thenew pressure setting of the pump 62 as set by the rotation of the shaft64, The motor-pump unit 60 will continue to operate as a motor to bringthe line 92 to its original position prior to paying-out. As themotor-pump unit 6 3 continues to operate, the setting on the pump 62 isdecreased to the original setting to maintain the original 8,000-poundtension. When the pressure on the line 92 reaches 8,000 pounds, whichwas the original tension on the line, the setting on the pump 62 is theoriginal predetcrmined amount and the pressure in the accumulator 72 isalso that original predetermined amount set by the hand wheel 95. Thetension on the tow line 92 is 8,000 pounds and the motor-pump unit 61'and pump 62 are then idle.

Assume now that the motor-pump unit 60 and pump 62 are idle on the line,and due to an externally created force, the tow line load decreasesbelow 8,000 pounds. The line will then begin to pay-in. The motor-pumpunit 6% will operate as a motor, pulling the line 92 in, utilizing thefluid under pressure in the accumulator 72. When the motor-pump unit 66is operated as a motor, the pressure in the accumulator 72 will dropbelow the setting of the variable capacity pump 62 set by the hand wheel95. As the motor-pump unit 60 continues to operate, the pressure settingon the pump 62 is decreased and the pump 62 is forced to operate at alower setting than that necessary to maintain an 8,000-pound tension onthe tow line 92. The line 92, due to external forces, then begins topay-out and the motor-pump unit 60 is operated in the reverse direction.As the motor-pump unit 60 operates in the reverse direction, thepressure in the accumulator 72 is increased, the pump 62 supplying thefluid to the accumulator 72, depending upon the new setting effected bythe rotation of the shaft 64. The motor-pump unit 60 continues tooperate until the tow line tension of 8,000 pounds is reached. If theline does not return to the original setting upon paying-out, then thesetting on the pump 62 will not have been returned to the originalsetting to eflect the predetermined pressure in the accumulator as setby the hand wheel 95. Due to the fact that there are fiuid losses in themotor-pump unit 60, the motor-piunp unit will continue to operate. in. areverse direction, paying-out until the setting on the pump 62 isreturned to that setting that maintains the pressure imthe accumulatorattheoriginal" predetermined amount;

The systenr'isthen returned tothe-- position where the load on -theline-92" is-8 ,000 pounds and the predetermined pressure iii the accumulatoris also reached. It is'seen that the length of the-line- 92 is alsoreturned to that length-prior to-the' line paying-in; Although thehydraulic system shown" in Fig 2 is automatic in operation, themotor-pump unit 60is provided'with a manually operated control lever 104for controlling the operationof the unit as desired when. the tow line92 operatively associated with the unit. is paying-out or paying-in.

Referring now to Fig; 4,- a further modified form of the present--invention is diagrammatically illustrated and, inthis form-oftheinvention, the hydraulic system is adapted to be utilized for; brakingand accelerating a vehicle or the like. As shownin Fig. 4, 7 the frameof a vehicle for use'witlra bus, truck, or the like, isgenerally'indi'cated at-1102 The frame 110 has mounted thereon suitablefrontwheels 112- and double rear wheels 114. A'priine-mover in; theformof an internal combustion engine 116is= positioned on" the framebetween the front wheels 1 12' and has joined thereto a transmission118. Coupled to-the; transmission 118 is a motor-pump unit 120- which,in this instance, isa fixed displacement unit. The-motor-pump unit 120is operatively connected through a drive shaft 122 to adifferential 124that, in turn, is operatively connected to the rear wheels 114. Themotorpump unit 120 communicates with a reservoir 126' through a fluidconduit 128, acheck valve 130'being interposed between the reservoir126' and motor-pump unit'120 in the fluid'conduit line 128. Themotor-pump unit 120 further communi'cateswith a hydraulic accumulator132' through fluidconduit lines 134, 136 and 138. The accumulator 132 isof that type described above in connectionwith- Figs. 1 and 2 whereinapro-charge fluid or gas-is contained inthe upper portion of theaccumulator; The accumulator 132 also communicates with the.motorpump:unit"120= through the fluid conduit 138, a fluid conduit; 140and the conduit 128 when the unit is to be operated as a motor. Aby-pass valve 142 connects thefluid conduit 128 to the fluid conduit 134and by-passes the-motive fluid when the motor-pump unit 120 is reversedas, for example, when the vehicle is moved in a reverse direction: Thereservoir 126 communicates with the accumulator 132 through a'fluidconduit 144; a brake valve 146 being interposed between the reservoir126 and and" accumulator 132 for controlling the direction of'the flowof thehydraulic fluid; A spring. loaded non-return valve 148. ispositioned in the fluid conduit 136 and prevents the-flowoffluidin'a'rreverse direction therein. A by-passiline 150 is adapted to directthe hydraulic fluid to-- the reservoir 126- through" a relief valve 152'when thepressuredn-the accumulator 132 exceeds the predetermined figure.The system is'completed by positioning a throttlevalve- 154 in-thefluidconduit 140' the throttle valve 1 54providingfor communication of theaccumulator'withthe motor-pump unit 120.

Inoperation of the system shown in Fig. 4, the internal combustionengine or prime mover 116' is adapted. to continuously drive themotor-pump unit 120 and operate the-unit as-a'pump; pumping fluid fromthe reservoir 126 through-the conduits 128 and 134 and returning thehydraulic-fluid to-the-reservoir 126 by way of the brake. valve 146' andfluid conduit 144. Thus, under normal operatingconditions, thefluidiscontinually recirculated through the reservoir 126'to the motor=pumpunit 120 V and? returned to the reservoir 126. During a brakingoperation, the'brakevalve-146 is closed and the motorpump: unit 120delivers fluidthrough the spring-loaded non-return valve 148 to-thehydraulic fluid accumulator 132: until the: pressure in the accumulatorreachesa predetermined amount; If the-braking cycle is continued, therelief valve;'1-52 opens andallows the hydraulic fluid to return to the.reservoir 126 under pressure equal to the pressure in the hydraulicfluid, accumulator 132. During.

the braking operatiomthe pressure in 1ine'134- is built up, thus'tendingto cause the shaft- 122 to be braked. In

an emergency, the mechanical brakes canbe utilized to" assist-inbringing the vehicle'to a rest position.

In the power operation, the throttle valve 154 is opened and the fluidunder pressure in the hydraulic fluid accumulator 132 passes through thethrottle valve 154 by way of fluid conduit 138, and then passes throughfluid con- 7 the vehicle to'thereby accelerate the drive shaft 122. The

hydraulic fluid then passes through the unit and through the brake valve46, which has been opened, and returned to the reservoir 126.

braked by closing the brake valve 146, the unit 'operates as a pump toreturn the fluid from the reservoir to the accumulator until thepredetermined pressure therein.

has been reached.

It is seen that the system illustrated in Fig. 4 will materially reducewear on brakes and give a greater impetusto starting or accelerating thevehicle. The system may be advantageously employed in connection withvehicles that constantly decelerate and accelerate, such as, forexample, buses, taxicabs, etc.

It will be obvious to those skilled in the art that various changes maybe made without departing from the spirit of the invention and thereforethe invention is not limited to what is shown in the drawings anddescribed termined by the rotation of said shaft is reached, and areservoir communicating with said motor-pump unit through a conduit,said accumulator supplying the hy-- draulic fluid under pressure locatedtherein to said motor.-

pump unit to rotate the shaft thereof, thereby operating said unit as amotor to perform work, the hydraulic fluid being directed to saidreservoir from said unit, the energy 7 accumulated in the shaft of saidunit thereafter reversing the rotation thereof to operate said unit as apump, saidunit pumping said fluid from said reservoir to'said'accw. V

mulator.

2.. In a hydraulic system, a hydraulic motor-pump'unit, an accumulatorcommunicating withsaid unit, a connecting. shaft attached at one end tosaid. hydraulic motorpump unit, a variable displacement pumpcommunicating: with said accumulator and supplying motive fluid theretountil: a predetermined pressure in said accumulator is' reached, saidconnecting shaft being operatively connected at its other end to saidvariable displacement pump for controlling the supply of motive fluidto' said. accumulator, the motive fluid in said accumulator beingdirected under pressure to said unit to operate said unit as a motor,thedirection of rotation of said unit being reversible to operate as apump for returning saidmotive fluid to saidaccumulator.

3; In a hydraulic system, a motor-pump unit, a rotat able. shaftattached to said unit, an accumulator containing motive fluid thereincommunicating with said unit to supply said fluid under pressurethereto, a variable" displacement pump communicating withsaidaccumulator to supply fluid'thereto until apredetermined pressureiisWhen the accumulator 132 is emptied of the fluid under pressure and thevehicle is again" reached therein, said variable displacement pump beingmechanically connected to said motor pump unit and controlled by therotation thereof the fluid under pressure in said accumulator enteringthe discharge side of said unit to operate said unit as a motor forcausing rotation of the shaft of said unit, the energy accumulated inrotating the shaft of said unit being utilized to rotate said shaft inthe opposite direction to draw said fluid into the suc tion side of saidunit for operating said unit as a pump, said unit thereby returning saidfluid to said accumulator.

4. In a hydraulic system, a motor-pump unit, a rotatable shaft attachedto said unit, a load connected directly to the shaft of said unit, saidunit thereby being responsive to the load on said shaft, an accumulatorcontaining motive fluid therein communicating with said unit, a variabledisplacement pump communicating with said accumulator and operativelyconnected to said unit, said unit rotating in response to the load onthe shaft thereof, said accumulator being responsive to the direction ofrotation of said unit and supplying fluid under pressure to said unit tooperate said unit as a motor, said pump being responsive to the rotationof said unit for supplying fluid to said accumulator until a pressuredetermined by the rotation of the shaft of said unit is reached, saidunit operating as a pump in response to the energy accumulated inrotating said shaft to return fluid to said accumulator.

5. In a hydraulic system as set forth in claim 4, wherein said pumpincludes a manually operated means for setting the pressure capacity ofsaid pump, and means operatively connected to the shaft of said unit andresponsive to the rotation thereof is provided for automaticallyadjusting the pressure capacity of said pump.

References Cited in the file of this patent UNITED STATES PATENTS2,382,437 Molly Aug. 14, 1945 2,554,381 Patterson May 22, 1951 2,576,359Putnam Nov. 27, 1951 2,752,754 Jaseph July 3, 1956

